How do digital answering machines work?

If you've read How CDs Work, then you know about how to store sound digitally. In a digital answering machine, these same principles are used to convert a caller's message into a stream of bytes. A microcontroller digitizes the caller's voice using an analog-to-digital converter and stores it in low-power RAM (random-access memory).

So let's say a caller leaves a 15-second message. That might translate into 30,000 bytes of digitized data. These bytes are stored at a specific address in RAM (see the How C Programming Works for a discussion on memory addresses). To play the message back, the microcontroller reads the 30,000 bytes from RAM and plays them through a digital-to-analog converter.

RAM is a high-speed memory device, so the microcontroller can erase one of the messages and easily move the other messages forward into the freed-up space.

Fed up with carrying a wallet full of cards and a full ring of keys? Before long, you might be able to keep all of that stuff in your phone. How is it possible, and is your information safe in your phone?